Ion beam incident angle detection assembly and method

ABSTRACT

In an ion implanter, a detector assembly is employed to monitor the ion beam current and incidence angle at the location of the work piece or wafer. The detector assembly includes a plurality of pairs of current sensors and a blocker panel. The blocker panel is coupled to the detector array to move together with the detector array. The blocker panel is also disposed a distance away from the sensors to allow certain of the beamlets that comprise the ion beam to reach the sensors. Each sensor in a pair of sensors measures the beam current incident thereon and the incident angle is calculated using these measurements. In this manner, beam current and incidence angle variations may be measured at the work piece site and be accommodated for, thereby avoiding undesirable beam current profiles.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of prior U.S. application Ser. No.12/568,781, filed Sep. 29, 2009, which is incorporated herein byreference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the invention relate to the field of semiconductor devicefabrication. More particularly, the present invention relates to anapparatus and method for measuring the incidence angle for an ion beamin an ion implanter.

2. Discussion of Related Art

Ion implantation is a process used to dope impurity ions into asemiconductor substrate to obtain desired device characteristics. Aprecise doping profile in a semiconductor substrate and associated thinfilm structure is critical for proper device performance. An ion beam isdirected from an ion source chamber toward a substrate. The depth ofimplantation into the substrate is based on the ion implant energy andthe mass of the ions generated in the source chamber. In addition, thebeam dose (the amount of ions implanted in the substrate) and the beamcurrent (the uniformity of the ion beam) can be manipulated through theuse of a mass analyzing magnet, a corrector magnet and one or moreacceleration and deceleration stages along the ion beam path to providea desired doping profile in the substrate. However, throughput ormanufacturing of semiconductor devices is highly dependent on theuniformity of the ion beam on the target substrate to produce thedesired device characteristics.

Generally, beam current, energy contamination and uniformity both of ionbeam current density and angle of implantation are the parameters thatjeopardize device throughput during semiconductor manufacturingprocesses. For example, if the beam current is too low, this will reducethe throughput of the implanter for a given total ion dose. Energycontamination occurs when there is a small fraction of the ion beam thatis at a higher energy than desired. This small fraction of the ion beamat a higher energy level will rapidly increase the depth of the desiredjunction that is formed in the substrate when creating an integratedcircuit and lead to degraded performance of the desired circuit profile.If the ion beam current density and angle of implantation are notuniform, there will be variations in the device properties formed acrossthe semiconductor substrate. These variations in beam current and angleof implantation can compromise the desired device characteristics whichcould produce lower manufacturing yields and lead to higher processingcosts. Thus, there is a need to control at least one or more of theseparameters to provide current uniformity for ion implantation systemswhen manufacturing semiconductor devices.

SUMMARY OF THE INVENTION

Exemplary embodiments of the present invention are directed to anapparatus for measuring the incidence angles of an ion beam in an ionimplanter. In an exemplary embodiment, an ion beam detector assemblyincludes a plurality of pairs of ion current sensors disposed along apath of an ion beam in an ion implanter. Each of the pairs of ioncurrent sensors is disposed on a detector array. The detector assemblystarts from a position outside of the ion beam path and moves across thebeam and terminates outside the beam path on the opposite side. As thedetector assembly moves across the beam a first of the current sensorsdetects a first beam current, and a second of the current sensorsdetects a second beam current where each of the first and seconddetected beam currents are used to determine an angle of incidence ofthe ion beam. A blocker panel is disposed a distance ‘d’ upstream fromthe plurality of pairs of ion current sensors. The blocker panel iscoupled to the detector array to move together with the detector array.The blocker panel is configured to block portions of the ion beam havinga first group of angles of incidence from reaching a first section ofeach of the ion current sensors and allowing portions of the ion beamhaving a second group of angles of incidence to reach a second sectionof each of the ion current sensors.

In an exemplary method of measuring angles of incidence of an ion beamincludes replacing a target wafer with an ion beam detector assemblyhaving a plurality of pairs of ion current sensors disposed on adetector array and a blocker panel coupled to the detector array. An ionbeam is provided and the detector assembly is moved across the ion beamby moving the detector array and the blocker panel together across theion beam. The beam current associated with the ion beam is detected bythe plurality of current sensors. The angle of incidence of the ion beamis calculated using the detected beam currents from the plurality ofcurrent sensors. The angles of incidence are analyzed to determine theuniformity of the ion beam. The beam current is adjusted based on thecalculated incidence angles.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a block diagram of a representative ion implanterincluding an incident angle detector assembly in accordance with anembodiment of the present invention.

FIG. 1A is a schematic view of the movement of the detector assemblywith respect to the ion beam path in accordance with an embodiment ofthe present invention.

FIG. 2 is a perspective view of an exemplary detector assembly inaccordance with an embodiment of the present invention.

FIG. 3A is a front view of the detector assembly of FIG. 2 in accordancewith an embodiment of the present invention.

FIG. 3B is an end view of the detector assembly of FIG. 2 in accordancewith an embodiment of the present invention.

FIG. 3C is a side view of the detector assembly of FIG. 2 in accordancewith an embodiment of the present invention.

FIG. 4 is a flow diagram illustrating an exemplary method of monitoringuniformity of ion implantation in accordance with an embodiment of thepresent invention.

DESCRIPTION OF EMBODIMENTS

The present invention will now be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the invention are shown. This invention, however, may be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art. In thedrawings, like numbers refer to like elements throughout.

FIG. 1 is a block diagram of an exemplary ion implanter 100 including anion source chamber 102. A power supply 101 supplies the required energyto source 102 which is configured to generate ions of a particularspecies. The ion source chamber 102 typically includes a heated filamentwhich ionizes a feed gas introduced into the chamber to form chargedions and electrons (plasma). The heating element may be, for example, aBernas source filament, an indirectly heated cathode (IHC) assembly orother thermal electron source. Different feed gases are supplied to theion source chamber to obtain ion beams having particular dopantcharacteristics. For example, the introduction of H₂, BF₃ and AsH₃ atrelatively high chamber temperatures are broken down into mono-atomshaving high implant energies. High implant energies are usuallyassociated with values greater than 20 keV. For low-energy ionimplantation, heavier charged molecules such as decaborane, carborane,etc., are introduced into the source chamber at a lower chambertemperature which preserves the molecular structure of the ionizedmolecules having lower implant energies. Low implant energies typicallyhave values below 20 keV.

The generated ions are extracted from the source through a series ofelectrodes 104 and formed into a beam 105 which passes through a massanalyzer magnet 106. The mass analyzer is configured with a particularmagnetic field such that only the ions with a desired mass-to-chargeratio are able to travel through the analyzer for maximum transmissionthrough a mass resolving slit and onto deceleration stage 108. Thedeceleration stage comprising multiple electrodes with defined aperturesthat allow the ion beam to pass. By applying different combinations ofvoltage potentials to these electrodes, the deceleration stagemanipulates the ion energies in the beam.

Corrector magnet 110 is disposed downstream of the deceleration stateand is energized to deflect ion beamlets in accordance with the strengthand direction of the applied magnetic field to provide a ribbon beamtargeted toward a work piece or substrate 114 positioned on a support orplaten. In other words, the corrector magnet shapes the ion beamgenerated from the deceleration stage into the correct form fordeposition onto the workpiece. In addition, the corrector magnet filtersout any ions from the beam that may have been neutralized whiletraveling through the beam line. In some embodiments, a seconddeceleration stage 112 may be disposed between corrector magnet 110 andtarget work piece 114. This second deceleration stage comprising adeceleration lens receives the ion beam from the corrector magnet andfurther manipulates the energy of the ion beam before it hits theworkpiece 114.

As the beam hits the work piece 114, the ions in the beam penetrates thework piece coming to rest beneath the surface to form a region ofdesired conductivity, whose depth is determined by the energy of theions. In order to ensure that the ions penetrate the work piece at adesired incident angle and beam current, system 100 includes detectorassembly 116 having a plurality of sensors such as, for example Faradaycups, configured to detect the beam current measured at various pointsalong the path through the ion beam 105. The changes in beam currentrelative to the various measured points using the detector assembly 116yields a measurement of the ion beam incident angle as described withrespect to the process outlined below. The detector assembly 116replaces work piece 114 and the profile measured at each of thesesensors is used to determine the angle of incidence of the beam 105.Based on these measurements, the profile may be modified to improveimplant uniformity. Once the desired beam current and incident angle isobtained, the detector assembly 116 is replaced with work piece 114 andthe detector assembly is removed from the beam line. In this manner,feedback from the detector assembly may be used to manipulateelectromagnets along the beam line to provide a desired beam profile.

FIG. 1A is a schematic drawing illustrating the movement of detectorassembly 116 from a starting position A to an end position B. Detectorassembly 116 starts from a position A outside of the ion beam path,moves horizontally across the beam 105 and terminates at a position Boutside the beam path on the opposite side thereof. As the assemblymoves across the beam 105 and the current values detected by each of thedetector elements is recorded. The position of the detector assembly 116as it moves across the beam is also recorded and associated with thecorresponding current value detected by the respective detector element.

FIG. 2 is a perspective view of detector assembly 116 including ablocker panel 210 and a graphite array 220 having Faradays defined byFaraday pixels 220 ₁ . . . 220 _(N) and Faraday bodies 221 ₁ . . . 221_(N) disposed therein. The blocker panel 210 is disposed a givendistance “d” away from the array 220. The Faradays are arranged in pairsalong the X axis and are configured to receive a portion of the ion beamnot blocked by panel 210. Each Faraday measures the beam current as theassembly 200 is moved in direction X. In particular, each Faradayreceives a portion of the analyzed beam 105 and produces an electricalcurrent based on the representative current thereof. Each Faraday isconnected to a current meter to detect the amperage (e.g. mA) and basedon the area of the respective Faraday pixel 220 ₁ . . . 220 _(N),determines the current (e.g. mA/cm2) of the ion beam received by theFaraday. For explanation purposes, the beam 105 shown in FIG. 2 is aportion of the beam typically incident on a work piece. The bodyportions 221 ₁ . . . 221 _(N) of the Faradays extend a distance indirection Z in order to prevent the beamlets of beam 105 which enterpixels 220 ₁ . . . 220 _(N) from escaping. As beam 105 is incident onFaraday pixels 220 ₁ and 220 ₂, the beam current is measured by therespective Faradays and the incident angle A of the beam 105 on theparticular pixels is calculated by using the following equation:A=ArcTan(((Ia−Ib)*w)/((Ia+Ib)*2d))  (Equation 1)where Ia and Ib are the beam currents measured at a first and second ofa pair of Faraday pixels (e.g. Faraday pixels 220 ₁ and 220 ₂), ‘w’ isthe width of a particular one of the array of Faraday pixels 220 ₁ . . .220 _(N) and d is the distance from blocker panel 210 to array 220 (asillustrated in FIGS. 3A-3C). Because of the different positions of eachof the pixels 220 ₁ . . . 220 _(N) along the array 220, each measuresdifferent amounts of the beam current depending on the angle ofincidence for the particular Faraday. In this manner, N/2 pairs ofFaradays are used to provide a two-dimensional array of incident anglesof beam 105 in direction Y based on the number of detectors in directionX. The two dimensional array of angles is used to adjust the lenses andmagnets in the ion implanter to obtain the desired beam angles incidenton a work piece. In addition, the larger the distance d, the greater theresolution of the incident angles. However, a process trade off existsbetween greater angle resolution versus detection of smaller incidentangles. The calculation of incidence angles can be repeated and theuntil the array of incidence angles is acceptable for a particularimplantation profile.

FIG. 3A is a front view of the detector assembly 116 shown in FIG. 2including a blocker panel 210 and graphite array 220 housing pairs ofFaraday pixels 220 ₁ . . . 220 _(N). Each of the pixels 220 ₁ . . . 220_(N) has a width “w”, a first portion of which is disposed behindblocker panel 210 and a second portion of which is not disposed behindblocker panel 210. Although part of a pixel is behind blocker panel 210,each pixel is configured to detect a portion of ion beam 105 incidentthereon. The pixels 220 ₁ . . . 220 _(N) are shown in pair-wise linearcolumns where the current detected by each pixel pair used to determinethe incident angle in accordance with Equation 1 above. A first blockersupport post 240 ₁ is connected to graphite array 220 and blocker panel210 at a first end of detector assembly 116. A second blocker supportpost 240 ₂ is connected to graphite array 220 and blocker panel 210 at asecond end of detector assembly 116. Blocker panel 210 is asubstantially rectangular piece of graphite, however alternativeconductive materials and shapes may be employed. In addition, blockerpanel 210 may also be capable of rotation away from array 220 about oneof the support posts 240. This may be done to allow calibration of thedetectors in the array.

Blocker panel 210 is configured to block beamlets of the incident ionbeam 105 from reaching the first portion of each Faraday pixel 220 ₁ . .. 220 _(N). For example, a first portion 220 a of pixel 220 ₂ which hasa width approximately w/2 is disposed behind blocker panel 210 and canonly receive beamlets of ion beam 105 which are incident thereon at anangle with respect to the planar surface of the array 220. In otherwords, beamlets of the ion beam 105 which are perpendicular to firstportion 220 a of pixel 220 ₂ will be blocked by blocker panel 210.Similarly, beamlets of the ion beam 105 which are less than orthogonalon pixel portion 220 a (i.e. toward pixel 220 ₁) will likewise beblocked from reaching pixel portion 220 a by blocker panel 210. However,second pixel portion 220 b of pixel 220 ₂ which is also has a width ofapproximately w/2 is not disposed behind blocker panel 210 and thereforeis configured to receive beamlets of the ion beam 105 which aresubstantially orthogonal to pixel portion 220 b and beamlets of the ionbeam 105 which are less than orthogonal to pixel portion 220 b. Thewidth of each of the pixel portions 220 a and 220 b may have alternativedimensions depending on the range of incident angles being detected.

The relationship of the Faraday pixels and the ion beam 105 isillustrated more clearly in FIG. 3B which is an end view of detectorassembly 116 taken in direction A. FIG. 3B illustrates blocker panel210, blocker support post 240 ₂ array 220, pixel pair 220 ₁ and 220 ₂and pixel bodies 221 ₁ and 221 ₂, respectively. By way of example,beamlets 105 ₁ . . . 105 ₄ are incident on Faraday pixels 220 ₁ and 220₂ of detector assembly 116. Beamlet portion 105 ₁ of ion beam 105 isincident on and received by pixel 220 ₂ at an incident angle. Beamletportion 105 ₂ is orthogonal to pixel 220 ₂ and is blocked by blockerpanel 210. Beamlet portion 105 ₃ of ion beam 105 is orthogonal to pixel220 ₁ and is blocked by blocker panel 210. Beamlet portion 105 ₄ of ionbeam 105 is incident on and received by pixel 220 ₁ at an incidentangle. In this example, each of the Faraday pixels 220 ₁ and 220 ₂detects the current density of the incident ion beam and the detectordetermines the incident angles in accordance with Equation 1 above.

FIG. 3C is a side view of detector assembly 116 illustrating thedistance d between blocker panel 210 and array 220. In particular,distance d is measured from first surface 210 a of blocker panel 210 tofirst surface 220 a of array 220. Support posts 240 ₁ and 240 ₂ aredisposed between first surface 220 a of array 220 and second surface 210b of blocker panel 210. Each of the support posts may extend intorespective bores (not shown) in blocker panel 210. Alternatively,support posts 240 ₁ and 240 ₂ may be adjustably configurable to vary thedistance d between blocker panel 210 and array 220. Faraday bodies 221 ₁. . . 221 _(N) extend from array 220 in order to prevent the beamlets ofbeam 105 which enter pixels 220 ₁ . . . 220 _(k) from escaping andthereby detecting the received beam current.

FIG. 4 is a flow diagram illustrating an exemplary method 300 ofmonitoring uniformity of an ion beam in an ion implantation system. Atstep 310, a target work piece is moved away from the ion beam and thedetector assembly replaces the work piece to tune a desired implantprofile. The detector is provided with a plurality of pairs of Faradaypixels to detect beam currents incident on the pixels. At step 320, thedetector assembly is moved horizontally through the ion beam. Thecurrent values of the beam incident on each of the pairs of Faradaypixels are recorded and stored at step 330. For example, the currentassociated with detector 220 ₁ is recorded and stored and the currentassociated with the corresponding other of the pair of detectors 220 ₂is recorded and stored. At step 340, the position of the detectorassembly for each of the current values in step 330 is recorded. Thepositions of the current measured at step 340 is adjusted to compensatefor the distance between the detector pairs at step 350. In other words,the detected currents will have positions that differ by the horizontalseparation of each of the detectors in a pair. Once the detectorassembly has passed completely through the ion beam at step 360, theassembly is stopped and the beam angles are calculated. In particular,the angle of incidence of the beam on each pair of the plurality ofpairs of detectors is calculated at step 370 using the formulaA=ArcTan(((Ia−Ib)*w)/((Ia+Ib)*2d)) where A is the incident angle, Ia andIb are the beam currents measured at a first and second of a pair ofFaraday pixels, ‘w’ is the width of a particular one of the array ofFaraday pixels and d is the distance from a blocker panel 210 to theFaraday array 220. This calculation at provides a two dimensional arrayof angles in the Y direction based on the number of detectors in the Xdirection based on the number of current measurements performed as thedetector assembly 116 moved across the ion beam. The angles of incidenceare analyzed to determine the uniformity of the ion beam at step 380. Atstep 390, the beam current is adjusted based on the two dimensionalarray of angles calculated by adjusting the lenses and magnets to obtainthe desired beam profile. This procedure may be repeated until the arrayof angles is acceptable indicating that the lenses and magnets in theion implanter is appropriate for the given profile.

While the present invention has been disclosed with reference to certainembodiments, numerous modifications, alterations and changes to thedescribed embodiments are possible without departing from the sphere andscope of the present invention, as defined in the appended claims.Accordingly, it is intended that the present invention not be limited tothe described embodiments, but that it has the full scope defined by thelanguage of the following claims, and equivalents thereof.

What is claimed is:
 1. An ion beam detector assembly comprising: aplurality of pairs of ion current sensors disposed along a path of anion beam in an ion implanter, each of said pairs of ion current sensorsdisposed on a detector array, a first of said pair of current sensorsdetecting a first beam current, and a second of said pair of currentsensors detecting a second beam current wherein each of said first andsecond detected beam currents is used to determine an angle of incidenceof the ion beam; and a blocker panel fixed to the detector array to movetogether in a fixed relationship with the detector array through the ionbeam, the blocker panel disposed a distance ‘d’ upstream from theplurality of pairs of ion current sensors, said blocker panel configuredto block portions of the ion beam having a first group of angles ofincidence from reaching a first section of each of said ion currentsensors and allowing portions of the ion beam having a second group ofangles of incidence to reach a second section of each of said ioncurrent sensors.
 2. The ion beam detector assembly of claim 1 furthercomprising multiple support posts fixing the blocker panel to thedetector array.
 3. The ion beam detector assembly of claim 1 whereineach of said sensors has a width “w”, wherein approximately w/2 of eachof said sensors is disposed underneath said blocker panel andapproximately w/2 of each of said sensor is not disposed underneath saidblocker panel.
 4. The ion beam detector assembly of claim 3 wherein theangle of incidence A is obtained using the following formula:A=ArcTan(((Ia−Ib)*w)/((Ia+Ib)*2d)) where Ia and Ib are the detected beamcurrents measured at the first and second of the pair of the ion currentsensors.
 5. The ion beam detector assembly of claim 3 wherein the anglesof incidence are a function of the distance “d” between the blockerpanel and the pairs of ion current sensors, width “w” of each of thesensors and the first and second detected beam currents.
 6. The ion beamdetector assembly of claim 1 wherein each of the sensors detects the ionbeam current as the assembly moves across the ion beam.
 7. The ion beamdetector assembly of claim 1 wherein the detector array is comprised ofgraphite.
 8. The ion beam detector assembly of claim 1 wherein theplurality of pairs of ion current sensors are Faraday cups each definedby a Faraday pixel and a Faraday body.
 9. The ion beam detector assemblyof claim 1 wherein the detector array has a predefined surface area andsaid blocker panel has a substantially rectangular shape such that saidblocker panel covers more than ½ the surface area of the detector array.10. A method of measuring angles of incidence of an ion beam comprising:replacing a target wafer with an ion beam detector assembly having aplurality of pairs of ion current sensors disposed on a detector arrayand a blocker panel fixed to the detector array; providing an ion beam;moving the ion beam detector assembly across the ion beam by moving thedetector array and the blocker panel together in a fixed relationshipacross the ion beam; detecting the beam current associated with each ofthe plurality of current sensors; calculating the angle of incidence oneach of the plurality of current sensors using the detected beamcurrents; analyzing the angles of incidence to determine the uniformityof the ion beam; and adjusting the beam current based on the calculatedincidence angles.
 11. The method of claim 10 wherein each of saidsensors has a width “w”.
 12. The method of claim 11 wherein the blockerpanel is disposed a distance “d” away from the plurality of pairs of ioncurrent sensors.
 13. The method of claim 12 wherein the step ofcalculating the angle of incidence further comprises using the followingformula: A=ArcTan(((Ia−Ib)*w)/((Ia+Ib)*2d)) where Ia and Ib are thedetected beam currents measured at first and second of the plurality ofpairs of the ion current sensors.